1. Field of the Invention
The invention relates to an improved process of cleaning, etching, or coating high aspect ratio structures. More particularly, the invention relates to a process whereby a liquid plug is initially forced down into a high aspect ratio structure and is then quickly ejected from the structure with enough force to dislodge and remove all contaminants.
2. Related Art
In the semiconductor industry, the formation of high aspect ratio structures on wafer surfaces is a common practice. These high aspect ratio structures can perform various functions, such as acting as trenches for capacitors. In particular, high aspect ratio structures or trenches are important to the function of the device. Therefore, it is essential that the trench can be cleaned, coated, or etched thoroughly for proper functioning. At present, methods for treating a malfunctioning high aspect ratio structure include applying a new coating over the existing, incomplete coating or electrically isolating the malfunctioning high aspect ratio structure. These alternative solutions are generally not regarded as optimally effective.
It is generally difficult to get materials into and out of high aspect ratio structures, such as trench capacitors, due to surface tension, contact angle, and certain unique geometric considerations. In particular, high aspect ratio structures can have a huge differential in dimensional ratio (i.e., 40:1 differential). The problems are exacerbated when the high aspect ratio structures are extremely small, such as those located on semiconductor wafers. There are methods disclosed in the prior art for cleaning, coating, and etching wafer surfaces which include megasonics, excimer laser beam irradiation, and condensed-phase processing.
Excimer laser beam irradiation is a vapor phase system that attempts to remove surface particles by using a laser beam to scan the substrate within which the trench is formed. Although effective, the process requires a scan of the entire substrate and has several significant drawbacks. First, and foremost, this process is only effective on relatively flat wafer surfaces. Second, excimer lasers are expensive and require significant additional costs to maintain and operate. Third, the scanning process itself may cause local thermal stresses that adversely affect the physical characteristics and performance of the substrate. Finally, this process is only applicable to particle removal.
Condensed-phase processing is a method for getting a reactant onto a wafer surface and then removing it. This process provides for suitable process gases to condense and form a film on a cool substrate surface. The condensation is followed by a pulsed process energy source which is used to thermally activate the surface and provide for rapid evaporation of the film. Although effective, this process is again only applicable to relatively flat wafer surfaces. In addition, this process is only effective on volatile species, and not for particle removal: it is believed that contaminants or foreign materials lodged in the trench structures are resistant to this evaporation cleaning process.
In recent technological efforts, attempts have been made to introduce sophisticated directional etching or deposition processes in commercial semiconductor fabrication. These processes incorporate the use of molecular beam technology. This technology has not been effective in, for example, providing uniform deposition, which is necessary for proper coating of high aspect ratio structures.
Therefore, there is a need for a better process of removing material from or coating material onto high aspect ratio structures. Such structures are becoming more and more common in many industries and, in particular, the semiconductor industry.